not really... If you want 'real' BC's Compare the .277 diameter 150 grain Nosler Accubond 'Long range' with a listed G1 BC of .625 and a round nose of the same weight with a BC closer to .25
So my 'imaginary' BC's are not very unrealistic. If you cast a completely flat faced bullet in .277 @ 150 grains it'd likely have a BC closer to the .2 I listed. Those numbers weren't that un-realistic (Albeit it was for the caliber and weight I used as an example)

So if you intentionally created a bullet to have a really bad BC, you could use it to prove that two bullet of the same weight and caliber can have drastically different BCs.

Who in god's name is going to cast a flat nose .277 bullet and use it for the purposes that are required for your "proof". Google "Reification Fallacy" or Reductio Ad Absurdum

The bullets and BCs that you list as "proof" essentially do not exist in .223/4 caliber. The highest BC I've ever seen for a .224 bullet is around 0.580 and that's a 90gr which wouldn't work in 95% of the worlds .223Rem and probably not a single FN5.7.

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Still happily answering to the call-sign Peetza.
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The problem, as you so eloquently put it, is choice.
-The Architect
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He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.